This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-43417, filed on Feb. 20, 2001 and a Japanese Patent Application 2002-40256, filed on Feb. 18, 2002, the entire content of which is incorporated herein by reference.
This invention generally relates to a bearing mechanism and a pump provided with the bearing mechanism. More particularly, this invention pertains to a bearing mechanism and a pump provided with the bearing mechanism for rotatably supporting a shaft applied with varying load.
Various electric motor-pumps have been already well known. An electric motor pump provided with a pair of pump pistons is disclosed as an example of the electric motor-pumps in a publication as a U.S. Pat. No. 5,895,207 (corresponding to a Japanese Patent No. 3078578). The pair of pump pistons is arranged opposite each other around a pump eccentric of a rotor shaft. The pair of pump pistons is slidably moved in accordance with a rotatable movement of the rotor shaft, whereby a volume of each fluid chamber defined by each piston is varied. Fluid is hence introduced into each fluid chamber or discharged therefrom.
The rotor shaft of the electric motor pump disclosed in the above publication operates the pair of pump pistons when the rotor shaft is rotated. The rotor shaft is hence applied with reactive load from the pair of pump pistons alternately. Therefore, a bearing supporting the rotor shaft is applied with the load as well.
In general, when even slight clearance is defined between a pump housing supporting the bearing and the bearing, the bearing may be displaced by the clearance in a direction of the load applied to the bearing and may collide with the pump housing. Especially, when the load is applied to the bearing alternately from opposite sides as disclosed in the above publication, the bearing may repeatedly collide with the pump housing. Accordingly, noise or vibration may occur due to the repeated collisions of the bearing with the pump housing.
In order to overcome the above described drawbacks, some methods have been conventionally utilized to clear the clearance between the bearing and the pump housing. For example, the clearance between the bearing and the pump housing can be sealed by pouring resin therein or by applying force from an outer periphery of the bearing or the housing toward the clearance for example by press-caulking or press-fitting.
However, according to the former method of pouring resin in the clearance, a manufacturing process for pouring resin and for hardening the resin is additionally required. Further, when the bearing is positioned at a central portion of the housing, a pouring circuit for pouring the resin to the bearing from an outside portion of the housing is additionally required. According to the latter method of applying force from the outer periphery of the bearing or the housing toward the clearance, the bearing may be deformed due to being applied with the undesirable force. Therefore, the bearing may not be rotated smoothly and unreasonable force may be applied to the rotor shaft. To overcome these drawbacks, the press-caulking or the press-fitting may be required to be accurately implemented for clearing the clearance and not for deforming the bearing. Further, this may require difficult assembling conditions and may cause low yield ratio. Therefore, manufacturing cost upon both methods may be increased to prevent noise or vibration.
Accordingly, known bearing mechanisms and electric motor-pumps are still susceptible of certain improvements with respect to supplying a bearing mechanism and the electric motor-pump which can restrain noise or vibration due to the collisions of the bearing with the pump housing at a low cost.
A bearing mechanism comprises a shaft applied with varying load, a bearing accommodated in a cylindrical bearing accommodating portion for supporting the shaft, and a biasing means. The biasing means is employed for biasing the bearing to be always in contact with at least a portion of an inner peripheral surface of the cylindrical bearing accommodating portion in a first direction different from a second direction in which the bearing is displaced in accordance with the varying load.
Further, according to another aspect of the present invention, a pump provided with a bearing mechanism comprises a rotor shaft pushed by a pair of pistons so as to displace the bearing supporting the rotor shaft. The bearing is biased by the biasing force of the biasing means in a radial direction to be always in contact with any one of portions of the cylindrical bearing accommodating portion so as to be displaced.
Further, according to another aspect of the present invention, a pump provided with a bearing mechanism comprises a bearing being inclined within the range of the clearance between the bearing and the cylindrical bearing accommodating portion due to the biasing force of the biasing means in the axial direction. That is, the bearing is accommodated in the cylindrical bearing accommodating portion having an axial direction being inclined relative to an axial direction of the cylindrical bearing accommodating portion.